Spectral biomarkers for chemoprevention of colonic neoplasia: a placebo-controlled double-blinded trial with aspirin.

OBJECTIVE: A major impediment to translating chemoprevention to clinical practice has been lack of intermediate biomarkers. We previously reported that rectal interrogation with low-coherence enhanced backscattering spectroscopy (LEBS) detected microarchitectural manifestations of field carcinogenesis. We now wanted to ascertain if reversion of two LEBS markers spectral slope (SPEC) and fractal dimension (FRAC) could serve as a marker for chemopreventive efficacy. DESIGN: We conducted a multicentre, prospective, randomised, double-blind placebo-controlled, clinical trial in subjects with a history of colonic neoplasia who manifested altered SPEC/FRAC in histologically normal colonic mucosa. Subjects (n=79) were randomised to 325 mg aspirin or placebo. The primary endpoint changed in FRAC and SPEC spectral markers after 3 months. Mucosal levels of prostaglandin E2 (PGE2) and UDP-glucuronosyltransferase (UGT)1A6 genotypes were planned secondary endpoints. RESULTS: At 3 months, the aspirin group manifested alterations in SPEC (48.9%, p=0.055) and FRAC (55.4%, p=0.200) with the direction towards non-neoplastic status. As a measure of aspirin's pharmacological efficacy, we assessed changes in rectal PGE2 levels and noted that it correlated with SPEC and FRAC alterations (R=-0.55, p=0.01 and R=0.57, p=0.009, respectively) whereas there was no significant correlation in placebo specimens. While UGT1A6 subgroup analysis did not achieve statistical significance, the changes in SPEC and FRAC to a less neoplastic direction occurred only in the variant consonant with epidemiological evidence of chemoprevention. CONCLUSIONS: We provide the first proof of concept, albeit somewhat underpowered, that spectral markers reversion mirrors antineoplastic efficacy providing a potential modality for titration of agent type/dose to optimise chemopreventive strategies in clinical practice. TRIAL NUMBER: NCT00468910.

Nanoscale changes in chromatin organization represent the initial steps of tumorigenesis: a transmission electron microscopy study.

BACKGROUND: Nuclear alterations are a well-known manifestation of cancer. However, little is known about the early, microscopically-undetectable stages of malignant transformation. Based on the phenomenon of field cancerization, the tissue in the field of a tumor can be used to identify and study the initiating events of carcinogenesis. Morphological changes in nuclear organization have been implicated in the field of colorectal cancer (CRC), and we hypothesize that characterization of chromatin alterations in the early stages of CRC will provide insight into cancer progression, as well as serve as a biomarker for early detection, risk stratification and prevention. METHODS: For this study we used transmission electron microscopy (TEM) images of nuclei harboring pre-neoplastic CRC alterations in two models: a carcinogen-treated animal model of early CRC, and microscopically normal-appearing tissue in the field of human CRC. We quantify the chromatin arrangement using approaches with two levels of complexity: 1) binary, where chromatin is separated into areas of dense heterochromatin and loose euchromatin, and 2) grey-scale, where the statistics of continuous mass-density distribution within the nucleus is quantified by its spatial correlation function. RESULTS: We established an increase in heterochromatin content and clump size, as well as a loss of its characteristic peripheral positioning in microscopically normal pre-neoplastic cell nuclei. Additionally, the analysis of chromatin density showed that its spatial distribution is altered from a fractal to a stretched exponential. CONCLUSIONS: We characterize quantitatively and qualitatively the nanoscale structural alterations preceding cancer development, which may allow for the establishment of promising new biomarkers for cancer risk stratification and diagnosis. The findings of this study confirm that ultrastructural changes of chromatin in field carcinogenesis represent early neoplastic events leading to the development of well-documented, microscopically detectable hallmarks of cancer.

Tumor suppressor FOXO3 mediates signals from the EGF receptor to regulate proliferation of colonic cells.

Epithelial proliferation, critical for homeostasis, healing, and colon cancer progression, is in part controlled by epidermal growth factor receptor (EGFR). Proliferation of colonic epithelia can be induced by Citrobacter rodentium infection, and we have demonstrated that activity of tumor suppressor FOXO3 was attenuated after this infection. Thus the aim of this study was to determine the contribution of FOXO3 in EGFR-dependent proliferation of intestinal epithelia and colon cancer cell lines. In this study we show that, during infection with C. rodentium, EGFR was significantly phosphorylated in colonic mucosa and Foxo3 deficiency in this model lead to an increased number of bromodeoxyuridine-positive cells. In vitro, in human colon cancer cells, increased expression and activation of EGFR was associated with proliferation that leads to FOXO3 phosphorylation (inactivation). Following EGFR activation, FOXO3 was phosphorylated (via phosphatidylinositol 3-kinase/Akt) and translocated to the cytosol where it was degraded. Moreover, inhibition of proliferation by overexpressing FOXO3 was not reversed by the EGFR signaling, implicating FOXO3 as one of the regulators downstream of EGFR. FOXO3 binding to the promoter of the cell cycle inhibitor p27kip1 was decreased by EGFR signaling, suggesting its role in EGFR-dependent proliferation. In conclusion, we show that proliferation in colonic epithelia and colon cancer cells, stimulated by EGFR, is mediated via loss of FOXO3 activity and speculate that FOXO3 may serve as a target in the development of new pharmacological treatments of proliferative diseases.

Polyethylene glycol-mediated colorectal cancer chemoprevention: roles of epidermal growth factor receptor and Snail.

Polyethylene glycol (PEG) is a clinically widely used agent with profound chemopreventive properties in experimental colon carcinogenesis. We reported previously that Snail/beta-catenin signaling may mediate the suppression of epithelial proliferation by PEG, although the upstream events remain unclear. We report herein the role of epidermal growth factor receptor (EGFR), a known mediator of Snail and overexpressed in approximately 80% of human colorectal cancers, on PEG-mediated antiproliferative and hence antineoplastic effects in azoxymethane (AOM) rats and HT-29 colon cancer cells. AOM rats were randomized to either standard diet or one with 10% PEG-3350 and euthanized 8 weeks later. The colonic samples were subjected to immunohistochemical or Western blot analyses. PEG decreased mucosal EGFR by 60% (P < 0.001). Similar PEG effects were obtained in HT-29 cells. PEG suppressed EGFR protein via lysosmal degradation with no change in mRNA levels. To show that EGFR antagonism per se was responsible for the antiproliferative effect, we inhibited EGFR by either pretreating cells with gefitinib or stably transfecting with EGFR-short hairpin RNA and measured the effect of PEG on proliferation. In either case, PEG effect was blunted, suggesting a vital role of EGFR. Flow cytometric analysis revealed that EGFR-short hairpin RNA cells, besides having reduced membrane EGFR, also expressed low Snail levels (40%), corroborating a strong association. Furthermore, in EGFR silenced cells, PEG effect on EGFR or Snail was muted, similar to that on proliferation. In conclusion, we show that EGFR is the proximate membrane signaling molecule through which PEG initiates antiproliferative activity with Snail/beta-catenin pathway playing the central intermediary function.

Antiproliferative effect of sulindac in colonic neoplasia prevention: role of COOH-terminal Src kinase.

Although the nonsteroidal anti-inflammatory drugs (NSAID) protection against colorectal cancer is well established, the molecular mechanisms remain unclear. We show herein that induction of the tumor suppressor gene COOH-terminal Src kinase (Csk) by NSAID is important for their antiproliferative and hence chemopreventive effects. In the azoxymethane-treated rat model of experimental colon carcinogenesis, sulindac treatment markedly induced Csk with a corresponding increase in inhibitory phosphorylation of Src (Tyr(527)). Sulindac-mediated Csk induction was replicated in the human colorectal cancer cell line HT-29, with a corresponding suppression of both Src kinase activity (63% of vehicle; P < 0.05) and E-cadherin tyrosine phosphorylation (an in vivo Src target). To determine the importance of Csk in NSAID antiproliferative activity, we stably transfected a Csk-specific short hairpin RNA (shRNA) vector into HT-29 cells, thereby blunting the sulindac-mediated Csk induction. These transfectants were significantly less responsive to the antiproliferative effect of sulindac sulfide (suppression of proliferating cell nuclear antigen was 21 +/- 2.3% in transfectants versus 45 +/- 4.23% in wild-type cells), with a corresponding mitigation of the sulindac-mediated G(1)-S-phase arrest (S-phase cells 48 +/- 3.6% versus 14 +/- 2.8% of vehicle respectively). Importantly, the Csk shRNA cells had a marked decrease in the cyclin-dependent kinase inhibitor p21(cip/waf1), a critical regulator of G(1)-S-phase progression (49% of wild-type cells). Moreover, although sulindac-mediated induction of p21(cip/waf1) was 113% in wild-type HT-29, this induction was alleviated in the Csk shRNA transfectants (65% induction; P < 0.01). Thus, this is the first demonstration that the antiproliferative activity of NSAID is modulated, at least partly, through the Csk/Src axis.

Prevention of colonic neoplasia with polyethylene glycol: A short term randomized placebo-controlled double-blinded trial.

Chemoprevention represents an attractive modality against colorectal cancer (CRC) although widespread clinical implementation of promising agents (e.g. aspirin/NSAIDS) have been stymied by both suboptimal efficacy and concerns over toxicity. This highlights the need for better agents. Several groups, including our own, have reported that the over-the-counter laxative polyethylene glycol (PEG) has remarkable efficacy in rodent models of colon carcinogenesis. In this study, we undertook the first randomized human trial to address the role of PEG in prevention of human colonic neoplasia. This was a double-blind, placebo-controlled, three-arm trial where eligible subjects were randomized to 8g PEG-3350 (n = 27) or 17g PEG-3350 (n = 24), or placebo (n = 24; maltodextrin) orally for a duration of six months. Our initial primary endpoint was rectal aberrant crypt foci (ACF) but this was changed during protocol period to rectal mucosal epidermal growth factor receptor (EGFR). Of the 87 patients randomized, 48 completed study primary endpoints and rectal EGFR unchanged PEG treatment. Rectal ACF had a trend suggesting potentially reduction with PEG treatment (pre-post change 1.7 in placebo versus -0.3 in PEG 8+ 17g doses, p = 0.108). Other endpoints (proliferation, apoptosis, expression of SNAIL and E-cadherin), previously noted to be modulated in rodent models, appeared unchanged with PEG treatment in this clinical trial. We conclude that PEG was generally well tolerated with the trial failing to meet primary efficacy endpoints. However, rectal ACFs demonstrated a trend (albeit statistically insignificant) for suppression with PEG. Moreover, all molecular assays including EGFR were unaltered with PEG underscoring issues with lack of translatability of biomarkers from preclinical to clinical trials. This data may provide the impetus for future clinical trials on PEG using more robust biomarkers of chemoprevention. TRIAL REGISTRATION: ClinicalTrials.gov NCT00828984.

Inducible nitric oxide synthase (iNOS) mediates the early increase of blood supply (EIBS) in colon carcinogenesis.

We have recently demonstrated that dramatic alteration in mucosal microvascular blood content termed early increase in blood supply (EIBS) is a hallmark of early colon carcinogenesis. In the current study, we elucidate the mechanism of EIBS by assessing iNOS/nitric oxide axis in the histologically normal colonic mucosa of rats treated with the colon-specific carcinogen, azoxymethane. We demonstrate that there was a strong temporal correlation between EIBS and iNOS expression/activity. Importantly, we also observed that short-term treatment with nitric oxide inhibitor abrogated EIBS. These data indicate that iNOS induction may have a critical role in augmenting the predysplastic mucosal blood supply and thereby fostering colon carcinogenesis.

Risk stratification of colon carcinogenesis through enhanced backscattering spectroscopy analysis of the uninvolved colonic mucosa.

INTRODUCTION: Our group has been interested in applying advances in biomedical optics to colorectal cancer risk stratification. Through a recent technological breakthrough, we have been able to harness information from enhanced backscattering spectroscopy, an optics phenomenon that allows quantitative, depth-selective analysis of the epithelial microscale/nanoscale architecture. In the present study, we investigated the ability of enhanced backscattering analysis of the preneoplastic mucosa to predict risk of colon carcinogenesis. METHODS: Enhanced backscattering analysis was done on intestinal mucosa at preneoplastic time points from two experimental models of colorectal cancer: the azoxymethane-treated rat and the multiple intestinal neoplasia (MIN) mouse. Data were analyzed using two previously validated spectral markers: spectral slope and principle components. We then did a pilot study on mucosal biopsies from 63 subjects undergoing screening colonoscopy. RESULTS: In the azoxymethane-treated rat, when compared with saline-treated controls, significant changes in the enhanced backscattering markers were observed as early as 2 weeks after azoxymethane treatment (before the development of aberrant crypt foci and adenomas). Enhanced backscattering markers continued to progress over time in a manner consonant with future neoplasia. These data were replicated in the preneoplastic MIN mouse mucosa. In humans, spectral slopes in the endoscopically normal cecum, midtransverse colon, and rectum were markedly reduced in patients harboring adenomas when compared with those who were neoplasia free. CONCLUSIONS: We show, for the first time, that enhanced backscattering analysis of an aliquot of uninvolved mucosa has the potential for predicting neoplastic risk throughout the colon in both experimental colorectal cancer models and humans.

Chemoprevention of colon carcinogenesis by polyethylene glycol: suppression of epithelial proliferation via modulation of SNAIL/beta-catenin signaling.

Polyethylene glycol (PEG) is one of the most potent chemopreventive agents against colorectal cancer; however, the mechanisms remain largely unexplored. In this study, we assessed the ability of PEG to target cyclin D1-beta-catenin-mediated hyperproliferation in the azoxymethane-treated rat model and the human colorectal cancer cell line, HT-29. Azoxymethane-treated rats were randomized to AIN-76A diet alone or supplemented with 5% PEG-8000. After 30 weeks, animals were euthanized and biopsies of aberrant crypt foci and uninvolved crypts were subjected to immunohistochemical and immunoblot analyses. PEG markedly suppressed both early and late markers of azoxymethane-induced colon carcinogenesis (fractal dimension by 80%, aberrant crypt foci by 64%, and tumors by 74%). In both azoxymethane-treated rats and HT-29 cells treated with 5% PEG-3350 for 24 hours, PEG decreased proliferation (45% and 52%, respectively) and cyclin D1 (78% and 56%, respectively). Because beta-catenin is the major regulator of cyclin D1 in colorectal cancer, we used the T-cell factor (Tcf)-TOPFLASH reporter assay to show that PEG markedly inhibited beta-catenin transcriptional activity. PEG did not alter total beta-catenin expression but rather its nuclear localization, leading us to assess E-cadherin expression (a major determinant of beta-catenin subcellular localization), which was increased by 73% and 71% in the azoxymethane-rat and HT-29 cells, respectively. We therefore investigated the effect of PEG treatment on levels of the negative regulator of E-cadherin, SNAIL, and observed a 50% and 75% decrease, respectively. In conclusion, we show, for the first time, a molecular mechanism through which PEG imparts its antiproliferative and hence profound chemopreventive effect.

Metabolic reprogramming of the premalignant colonic mucosa is an early event in carcinogenesis.

BACKGROUND: Colorectal cancer (CRC) is the second leading cause of cancer-related mortality in the United States. There is an increasing need for the identification of biomarkers of pre-malignant and early stage CRC to improve risk-stratification and screening recommendations. In this study, we investigated the possibility of metabolic and mitochondrial reprogramming early in the pre-malignant colorectal field. METHODS: Rectal biopsies were taken from 81 patients undergoing screening colonoscopy, and gene expression of metabolic and mitochondrial markers were assessed using real time quantitative PCR. Validation studies were performed in two different animal models of colon carcinogenesis: Pirc rats and AOM-treated rats. RESULTS: We found evidence of a Warburg effect in the normal-appearing rectal mucosa of patients harboring precancerous lesions elsewhere in the colon compared to control patients, with a significant increase in HIF1α, SLC2A1 (referred to as GLUT1), PKM2, and LDHA. We also found evidence of early mitochondrial changes in the colorectal field of patients harboring pre-cancerous lesions, with significantly increased mitochondrial gene expression of DRP1 (fission), OPA1 (fusion), PGC1-α (biogenesis), UCP2 (uncoupling) and mtND1 (copy number). Similar results were observed in the two different animal models. CONCLUSIONS: These results demonstrate for the first time evidence of early Warburg-like metabolic changes as well as changes in mitochondrial function, dynamics and mtDNA copy number in endoscopically normal premalignant colorectal mucosal field. These findings provide an opportunity for the development of metabolic biomarkers that could be used for improving screening recommendations and risk-stratification. This also provides a potential target for novel chemopreventive strategies in the pre-malignant colorectal field.

Low-coherence enhanced backscattering: review of principles and applications for colon cancer screening.

The phenomenon of enhanced backscattering (EBS) of light, also known as coherent backscattering (CBS) of light, has been the object of intensive investigation in nonbiological media over the last two decades. However, there have been only a few attempts to explore EBS for tissue characterization and diagnosis. We have recently made progress in the EBS measurements in tissue by taking advantage of low spatial coherence illumination, which has led us to the development of low-coherence enhanced backscattering (LEBS) spectroscopy. In this work, we review the current state of research on LEBS. After a brief discussion of the basic principle of EBS and LEBS, we present an overview of the unique features of LEBS for tissue characterization, and show that LEBS enables depth-selective spectroscopic assessment of mucosal tissue. Then, we demonstrate the potential of LEBS spectroscopy for predicting the risk of colon carcinogenesis and colonoscopy-free screening for colorectal cancer (CRC).

Ursodeoxycholic acid inhibits Ras mutations, wild-type Ras activation, and cyclooxygenase-2 expression in colon cancer.

K-ras mutations occur frequently in colon cancer and contribute to autonomous growth. In the azoxymethane (AOM) model of colon cancer, in addition to K-ras mutations, we have shown that wild-type (WT) Ras can be activated by upstream pathways, including, e.g., signaling by ErbB receptors. Tumors with mutant or activated WT Ras had increased cyclooxygenase-2 (Cox-2) expression. We have also shown that ursodeoxycholic acid (UDCA) prevented AOM-induced colon cancer and suppressed Cox-2 induction. In this study, we examined the role of Ras in Cox-2 inhibition by UDCA. Rats were fed AIN-76A chow alone, or supplemented with 0.4% UDCA, and received 20 mg/kg AOM i.p. weekly x 2 weeks. At 40 weeks, rats were sacrificed, and tumors were harvested. K-ras mutations were assessed by primer-mediated RFLP, allele-specific oligonucleotide hybridization, and direct DNA sequencing. Ras was immunoprecipitated and defined as activated if [Ras - GTP/(Ras - GTP + Ras - GDP)] was >3 SD above normal colonocytes. Cox-2 mRNA was determined by reverse transcription-PCR, and protein expression was assessed by Western blotting and immunostaining. In the AOM alone group, Ras was activated by mutations in 8 of 30 (27%) tumors, and WT Ras was activated in 7 of 30 (23%) tumors. UDCA significantly suppressed the incidence of tumors with mutant Ras (1 of 31, 3.2%; P < 0.05) and totally abolished the development of tumors with activated WT Ras (0 of 10; P < 0.05). In the AOM alone group, Cox-2 was up-regulated >50-fold in tumors with normal Ras activity and further enhanced in tumors with mutant or signaling-activated Ras. UDCA significantly inhibited Cox-2 protein and mRNA levels in tumors with normal Ras activity. In summary, we have shown for the first time that UDCA suppressed the development of tumors with Ras mutations and blocked activation of WT Ras. Furthermore, UDCA inhibited Cox-2 induction by Ras-dependent and -independent mechanisms.

Higher Order Chromatin Modulator Cohesin SA1 Is an Early Biomarker for Colon Carcinogenesis: Race-Specific Implications.

Alterations in high order chromatin, with concomitant modulation in gene expression, are one of the earliest events in the development of colorectal cancer. Cohesins are a family of proteins that modulate high-order chromatin, although the role in colorectal cancer remains incompletely understood. We, therefore, assessed the role of cohesin SA1 in colorectal cancer biology and as a biomarker focusing in particular on the increased incidence/mortality of colorectal cancer among African-Americans. Immunohistochemistry on tissue arrays revealed dramatically decreased SA1 expression in both adenomas (62%; P = 0.001) and adenocarcinomas (75%; P = 0.0001). RT-PCR performed in endoscopically normal rectal biopsies (n = 78) revealed a profound decrease in SA1 expression in adenoma-harboring patients (field carcinogenesis) compared with those who were neoplasia-free (47%; P = 0.03). From a racial perspective, colorectal cancer tissues from Caucasians had 56% higher SA1 expression than in African-Americans. This was mirrored in field carcinogenesis where healthy Caucasians expressed more SA1 at baseline compared with matched African-American subjects (73%; P = 0.003). However, as a biomarker for colorectal cancer risk, the diagnostic performance as assessed by area under ROC curve was greater in African-Americans (AUROC = 0.724) than in Caucasians (AUROC = 0.585). From a biologic perspective, SA1 modulation of high-order chromatin was demonstrated with both biophotonic (nanocytology) and chromatin accessibility [micrococcal nuclease (MNase)] assays in SA1-knockdown HT29 colorectal cancer cells. The functional consequences were underscored by increased proliferation (WST-1; P = 0.0002, colony formation; P = 0.001) in the SA1-knockdown HT29 cells. These results provide the first evidence indicating a tumor suppressor role of SA1 in early colon carcinogenesis and as a risk stratification biomarker giving potential insights into biologic basis of racial disparities in colorectal cancer. Cancer Prev Res; 9(11); 844-54. ©2016 AACR.

Down-regulation of the tumor suppressor gene C-terminal Src kinase: an early event during premalignant colonic epithelial hyperproliferation.

Hyperproliferation of the premalignant epithelium is critical for colonic carcinogenesis; however the mechanisms remain largely unexplored. We report herein that prior to occurrence of neoplastic lesions in the azoxymethane-rat model of colon carcinogenesis; the tumor suppressor gene C-terminal Src kinase (Csk) was down-regulated with a concomitant increase in Src activity. Furthermore, pharmacological or genetic (RNA interference) inhibition of Csk resulted in increased proliferation in colon cancer cell lines through the mitogen-activated protein kinase dependent pathway. Thus, we demonstrate, for the first time, that Csk suppression is an important early event in colorectal cancer pathogenesis.

Spectral markers in preneoplastic intestinal mucosa: an accurate predictor of tumor risk in the MIN mouse.

BACKGROUND: We have reported recently that microarchitectural analysis of the histologically normal mucosa using a novel optics technology, four-dimensional elastic light scattering fingerprinting (ELF), provided unprecedented sensitivity for early detection of colon carcinogenesis. In the present study, we explored the ability of four-dimensional ELF to identify an inherited predisposition to colorectal cancer, an issue of considerable importance for optimizing population screening strategies. METHODS: We used the MIN mouse, a model whose germ line adenomatous polyposis coli truncation leads to spontaneous intestinal tumorigenesis, thus replicating the human syndrome, familial adenomatous polyposis. Spectral markers were assessed by four-dimensional ELF analysis in MIN mice at preneoplastic time points and compared with age-matched controls (C57BL6 mice with wild-type adenomatous polyposis coli). To assess the responsiveness of spectral markers to chemopreventive agents, a subset of MIN mice was supplemented with celecoxib 1,500 ppm. RESULTS: Spectral slope, fractal dimension, and principal component 3 were dramatically altered in the uninvolved MIN mouse mucosa at the earliest time points. Furthermore, alteration in spectral variables increased over time, consonant with the microarchitectural underpinnings of subsequent tumorigenesis. Additionally, these markers spatially correlated with future adenoma development (small intestine > colon). Short-term treatment with the potent chemopreventive agent, celecoxib, resulted in near normalization of fractal dimension and principal component 3. CONCLUSIONS: We report, for the first time, that spectral markers, assayed by four-dimensional ELF, were able to sensitively identify a genetic predisposition for intestinal tumorigenesis before the occurrence of phenotypic manifestations. Moreover, the reversal of spectral markers by celecoxib treatment supports the neoplastic relevance.

The nonsteroidal anti-inflammatory drug, nabumetone, differentially inhibits beta-catenin signaling in the MIN mouse and azoxymethane-treated rat models of colon carcinogenesis.

The mechanisms through which beta-catenin signaling is inhibited during colorectal cancer chemoprevention by nonsteroidal anti-inflammatory agents is incompletely understood. We report that nabumetone decreased uninvolved intestinal mucosal beta-catenin levels in the MIN mouse with a concomitant increase in glycogen synthase kinase (GSK)-3beta levels, an enzyme that targets beta-catenin for destruction. However, in the azoxymethane-treated rat, where beta-catenin is frequently rendered GSK-3beta-insensitive, nabumetone failed to alter beta-catenin levels but did decrease beta-catenin nuclear localization and transcriptional activity as gauged by cyclin D1. In conclusion, we demonstrate that the differential mechanisms for beta-catenin suppression may be determined, at least partly, by GSK-3beta.

Down-regulation of SNAIL suppresses MIN mouse tumorigenesis: modulation of apoptosis, proliferation, and fractal dimension.

OBJECTIVES: Emerging evidence implicates the SNAIL family of transcriptional repressors in cancer development; however, the role of SNAIL in colorectal cancer has not been established. To investigate the importance of SNAIL in colorectal carcinogenesis, we examined the phenotypic and cellular consequences of SNAIL down-regulation in the MIN mouse. METHODS: Twenty-eight male MIN mice were randomized to treatment with an antisense phosphorodiamidate morpholino oligomer (AS-PMO) to SNAIL, saline, or a scrambled sequence control for 6 weeks. Tumors were scored and the molecular/cellular effects of anti-SNAIL treatment were evaluated through immunohistochemical analysis of the uninvolved intestinal mucosa for SNAIL and E-cadherin levels along with rates of apoptosis and proliferation. Furthermore, microarchitectural alterations were determined through measurement of fractal dimension. RESULTS: In the uninvolved mucosa, SNAIL AS-PMO treatment moderately decreased SNAIL protein when compared with saline-treated animals (immunohistochemistry scores 3.0 +/- 0.8 versus 2.1 +/- 0.6, respectively; P=0.01) with a concomitant increase in E-cadherin expression (1.8 +/- 0.6 versus 2.4 +/- 0.5; P < 0.05). Anti-SNAIL PMO, but not scramble control, resulted in a significant decrease in both total tumor number and incidence of tumors >2 mm (22% and 54%, respectively; P < 0.05). Furthermore, this was accompanied by an increased apoptosis rate (2-fold), decreased proliferation (3-fold), and normalization of the fractal dimension in the uninvolved intestinal mucosa. CONCLUSIONS: We show, for the first time, that SNAIL overexpression is important in intestinal tumorigenesis. While this PMO regimen afforded modest SNAIL suppression and hence tumor reduction, this provides compelling evidence for the role of SNAIL overexpression in colonic neoplasia.

Ursodeoxycholic acid inhibits the initiation and postinitiation phases of azoxymethane-induced colonic tumor development.

Colonic tumorigenesis involves the processes of initiation and promotion/progression from normal epithelial cells to tumors. Studies in both humans and experimental models of colon cancer indicate that secondary bile acids promote tumor development. In contrast, we have demonstrated previously that another bile acid, ursodeoxycholic acid (UDCA), inhibits the development of azoxymethane (AOM)-induced colon cancer in rats. More recently, we have shown that UDCA inhibits AOM-induced hyperproliferation, and aberrant crypt formation and growth. In our previous studies, we supplemented UDCA throughout the experiment. The efficacy of a chemopreventive agent may depend on the timing of administration, which has important clinical implications. In the present investigation, we examined the ability of UDCA, when administered only in the initiation or the promotion/progression phase, to block tumor development. Male Fisher 344 rats were divided in a 2 x 3 factorial design, with animals receiving AOM or vehicle, and fed an unsupplemented diet or diet supplemented with 0.4% UDCA in the initiation or promotion/progression phase. Thirty-two weeks later, rats were sacrificed and tumor histology determined, and colons were examined for aberrant crypt foci (ACF). In the carcinogen-treated dietary control group, tumor incidence was 72.3%, and tumor multiplicity was 1.9 tumors per tumor-bearing rat. UDCA, in the initiation or promotion/progression phase, significantly decreased tumor incidence to 46.2% and 38.4% (P < 0.05), respectively; and tumor multiplicity to 1.4 and 1.3 tumors per tumor-bearing rat (P < 0.05), respectively. UDCA did not alter tumor size, histology, or location, although there were trends for smaller tumors and less advanced histological grades in the group given UDCA during the promotion phase. UDCA, in the initiation but not the promotion phase, inhibited ACF formation and growth. In summary, UDCA significantly inhibited AOM-induced colonic carcinogenesis during either tumor initiation or in the promotion/progression phase. In contrast, UDCA inhibited ACF formation only when administered in the initiation phase, suggesting that the mechanisms of chemoprevention by this bile acid differ in these two phases.

Ursodeoxycholic acid and F(6)-D(3) inhibit aberrant crypt proliferation in the rat azoxymethane model of colon cancer: roles of cyclin D1 and E-cadherin.

We have previously demonstrated that ursodeoxycholic acid(UDCA) and a fluorinated analogue of vitamin D(3), F(6)-D(3),inhibited colonic carcinogenesis in the azoxymethane (AOM) model. Generalized colonic mucosal hyperproliferation and aberrant crypt foci (ACF) are intermediate biomarkers of colon cancer. Using these biomarkers, in this study we examined the anticarcinogenic mechanisms of these chemopreventive agents. Rats were maintained on AIN-76A chow or supplemented with 0.4% UDCA or F(6)-D(3) (2.5 nmol/kg chow) and treated weekly with AOM 20 mg i.p./kg wt or saline x 2 weeks. F(6)-D(3) was continued for an additional 2 weeks and UDCA for the duration of the study. At 40 weeks, animals received bromodeoxyuridine (BrdUrd) i.p. 2 h before sacrifice. A portion of each tumor was fixed in formalin and the remainder flash frozen. Colons were divided longitudinally and half-fixed in formalin and half in ethanol. The size and location of methylene blue-stained ACF were recorded. Cell proliferation (BrdUrd labeling) and apoptosis (terminal deoxynucleotidyl transferase-mediated nick end labeling assay) were measured in colonic crypts and tumors. Protein expression levels of several regulators of cell proliferation were analyzed by immunostaining and Western blotting. Colonic crypt cyclin D1 and E-cadherin mRNA levels were measured by real-time PCR. In saline injected controls, neither UDCA nor F(6)-D(3) alone had any effect on cytokinetic parameters or on the expression of mitogenic regulators. AOM significantly increased the proliferation (percentage of BrdUrd-positive cells) of both ACF (23.1 +/- 1.7%) and non-ACF crypts (17.6 +/- 1.6%), compared with normal colonic crypts (4.5 +/- 0.8%; P < 0.05). This hyperproliferation was accompanied by a 5-fold increase in cyclin D1 and >50% decrease in E-cadherin protein (P < 0.05) in ACF, both of which are predicted to be growth-enhancing alterations. UDCA and F(6)-D(3) significantly (P < 0.05) inhibited AOM-induced crypt cell hyperproliferation, ACF development, and tumor burden. These chemopreventive agents also significantly blocked AOM-induced alterations in cyclin D1 and E-cadherin protein in ACF and tumors. In ACF, changes in mRNA levels of cyclin D1, but not E-cadherin, paralleled alterations in protein expression. Cyclooxygenase-2 and inducible nitric oxide synthase were increased in AOM tumors but not in ACF, and these changes were blocked by UDCA and F(6)-D(3). UDCA and F(6)-D(3) significantly inhibited ACF development and hyperproliferation, in part, by preventing carcinogen-induced alterations in cyclin D1 and E-cadherin. In established tumors, UDCA and F(6)-D(3) also limited inductions of cyclooxygenase-2 and inducible nitric oxide synthase, which together with their effects on cyclin D1 and E-cadherin, contribute to their chemopreventive actions.

Polyethylene glycol inhibits intestinal neoplasia and induces epithelial apoptosis in Apc(min) mice.

Efficacy of a safe and clinically utilized polyethylene glycol formulation (PEG-3350) to suppress intestinal tumors was investigated in the Apc(min) mouse-model of experimental carcinogenesis. Furthermore, based on our previous finding on the induction of apoptosis in HT-29 cells by PEG, we evaluated its ability to stimulate epithelial cell apoptosis in both Apc(min) mouse as well as AOM-treated rat as a potential molecular mechanism of chemoprevention. Twenty-two Apc(min) mice were randomized equally to PEG or vehicle (control) supplementation. Tumors were scored and uninvolved intestinal mucosal apoptosis was assayed using a modified terminal deoxynucleotidyl transferase-mediated nick end-labeling (TUNEL) assay and by immunohistochemical detection of cleaved caspase-3. Supplementation of Apc(min) mice with 10% PEG 3350 (in drinking water) resulted in a 48% (P<0.05) reduction in intestinal tumor burden and induced 2-3 fold increase in mucosal apoptosis. Dietary supplementation of polyethylene glycol (5%) also stimulated colonic mucosal apoptosis 4-5 fold in AOM-treated rats, the regimen that we previously reported to reduce tumor burden by 76% (P<0.05). In summary, we demonstrate, for the first time, that PEG does protect against Apc(min) mouse tumorigenesis. The correlation between pro-apoptotic actions and chemopreventive efficacy of PEG in these models strongly implicates induction of apoptosis as one of the impending mechanisms of chemoprevention.